The International Criminal Court said on Wednesday that it would not yet open a probe into alleged crimes committed by the Islamic State group in Iraq and Syria, including genocide, as it lacks jurisdiction, AFP reports.

Iraq and Syria have not signed the ICC's founding Rome Statute that would give the court jurisdiction, but the ICC could prosecute some of the thousands of foreign ISIS fighters who are nationals of countries that have signed up.

Crimes of "unspeakable cruelty" including mass executions, sexual slavery, rape, torture and mutilation have been reported and genocide alleged, chief prosecutor Fatou Bensouda said in a statement.

As a result, her office has been assessing the prospect of exercising "personal jurisdiction" over foreign ISIS fighters, including from Tunisia,Jordan, Britain, France, Germany, Belgium, the Netherlands and Australia, she said.

However, the ISIS group is "primarily led by nationals of Iraq and Syria... thus, at this stage, the prospects of my office investigating and prosecuting those most responsible... appear limited."

"I have come to the conclusion that the jurisdictional basis for opening a preliminary examination into this situation is too narrow at this stage," Bensouda said.

The United Nations Security Council could refer the situation in Iraq and Syria to the ICC, as happened with Libya in 2011, Bensouda said, and countries with nationals who are ISIS terrorists could also launch their own prosecutions.

The prosecutor said in an interview in November that she was weighing bringing war crimes charges against Islamic State jihadist fighters, saying she had received files from several countries.

Islamic State terrorists have carried out a wave of abuses in areas they control in Iraq and Syria, including public beheadings, mass executions, enslavement and rape.

ISIS not under jurisdiction...but non-state PA is?

The ICC's decision not to prosecute ISIS contrasts sharply with its decision to prosecute Israel for alleged "war crimes" in the Palestinian Authority (PA) - even though the latter is not technically a state.

But the move has also paved the way for the PA to bear the legal brunt of its terrorism against Israel - and the evidence and condemnations have accumulated.

Since the declaration, Shurat HaDin – Israel Law Center has already launched lawsuits against Abbas and Hamas leaders at the ICC.

Many have noted that by joining the ICC the PA has opened itself up to lawsuits - every missile fired on Israel by the PA's unity partner Hamas, and indeed by PA chairman Mahmoud Abbas's Fatah, constitutes a war crime.

Specifically, a Palestinian Arab source admitted to the possibility of the ICC bid backfiring while speaking to Maariv last week, noting "Palestinians can make a claim against the settlements, but it's doubtful that a claim regarding the recent war in Gaza won't bring about a counter-suit from Israel, which is preparing for this."

"The Israelis have prepared stacks of paperwork on conduct during Operation Protective Edge, including claims of Hamas rocket fire and Palestinian groups shooting from schools and other civilian buildings. This could lead to a suit against Hamas leaders who control the Gaza Strip," the source added.